The use of electric components which are operated at high voltages (more than 200 V), or which may be subject to high-voltage peaks, requires the adherence to specified distances between the connecting contacts so as to ensure a safe operation. Here, a difference has to be made between the air gap and the creepage distance. The air gap is defined as the shortest distance in the air between two conductive parts. The creepage distance is defined as the shortest distance along the surface of an insulating material between two conductive parts. In general, the creepage distance for a certain voltage value has to be clearly longer than the air gap. The minimum requirements for the required air gaps, respectively, creepage distances depend on the used insulating materials, on the contamination category and the occurring voltages. The required values for the minimum air gap and the minimum creepage distance are specified, for instance, in DIN EN 60 558-2-15.
FIG. 1 shows an example of a transformer housing. FIG. 1a shows a perspective view from the top, and FIG. 1b shows a perspective view from the bottom. FIG. 1c shows a transparent lateral view of the housing, with a view to the coil 360 in the interior. The dashed line in FIG. 1c indicates the thickness of the housing wall of the hollow housing.
The housing is a substantially cylindrical hollow body open on one side. The open side defines the bottom surface OBF. The closed lid GD is positioned opposite the open bottom surface OBF. Contact pins 320a, 320b, 320c and 320d are embedded in the housing, at the edge of the open bottom surface OBF, and project vertically out of the bottom surface. The coil form 360 is inserted into the hollow space of the housing through the open bottom surface OBF, and the connecting wires 361 and 362 of the coil are electrically connected to the contact pins 320a-320d. The hollow space between the coil form and the open bottom surface OBF is filled, at least partially, with an electrically insulating filling compound 370.
Thus, the air gap realized for the housing 300 in FIG. 1 is the distance between two contact pins, e.g. between pin 320a and in 320d. The creepage distance additionally includes two times the distance A between the filling material 370 and the attachment 380 of the connecting wire 361 to the contact pin 320a. Hence, the arrangement shown in FIG. 1c has a creepage distance that is longer by about 25% than the air gap. As the creepage distance at a specific desired operating voltage has to be clearly higher than the air gap, subject to the degree of contamination and insulating materials used, the electric strength is substantially determined by the creepage distance. Thus, if the improvement of the electric strength of the housing 300 of FIG. 1 is desired, this may be achieved by increasing the creepage distance.
This is realized, for instance, in the housing according to FIG. 2. FIG. 2a shows a perspective view of the housing from the top, and FIG. 2b shows a partial cutaway lateral view of the housing, with a view to the coil 260. As opposed to the housing body 310 of FIG. 1, the housing body 210 is open towards the top, with an open lid surface ODF. Electric contact pins 220a, 220b are embedded in the closed bottom GB. The connecting wires 261 and 262 of the coil 260 are passed through the open lid surface ODF over the upper edge of the housing and along the outside of the housing to the contact pins 220a and 220b. FIG. 2b shows two possible embodiments for laying the connecting leads 261 and 262. Connecting lead 261 is guided inside the housing wall. Connecting lead 262 is guided outside the housing. The dashed lines 260a and 262a in FIG. 2b show the covered parts of the coil 260 and of the connecting wire 262. As opposed to the housing of FIG. 1 the creepage distance in FIG. 2b is increased by double the height of the housing. Similar to the housing of FIG. 1, the hollow space in the housing of FIG. 2 between the coil 260 and the open lid surface ODF is filled, at least partially, with an insulating filling material (not shown in FIG. 2b).
Although the creepage distance in the housing of FIG. 2 is clearly extended as opposed to the housing of FIG. 1 the overall height of the housing of FIG. 2 has to be relatively high in order to provide the room for the filling material for closing the open lid. In comparison with the prior art a housing would be desirable that has a low design and an extended creepage distance and air gap.